According to the so-called “contrast method”, focus control is performed based on a contrast of a region in a captured image that is to be brought into focus (hereinafter referred to as a “focus point search region”). More specifically, according to the contrast method, a focus lens is determined as being in an in-focus state when the contrast of the focus point search region becomes highest. In the meantime, there are many image capture devices that are provided with a face detection function of detecting a region including a person's face in a captured image. Such image capture devices set the region detected by face detection as the focus point search region in the captured image, and obtain a captured image that is appropriate in the sense that the person's face is brought into focus by performing focus control according to the contrast method.
Face detection, however, is a technology of capturing characteristic features of a person's eye, nose, mouth, etc. As such, generally speaking, only faces facing a limited range of directions in a captured image can be detected according to face detection. For instance, a face of a person facing backwards in a captured image or a face of a person facing sideways such that his/her eyes are hidden in a captured image cannot be detected by utilizing face detection. As such, in a case where a moving image is being shot while the focus point is being set to a person, for instance, face detection of the person's face fails when the person faces backwards in the midst of the shooting. This results in unstable focus (i.e., a state where the point in a captured image keeps changing unstably and the focus lens cannot be kept in the in-focus state). Similarly, when a person enters an image-capturing frame of an image capture device from outside the frame while a moving image is being shot, the focus point is not set to the person until the person turns his/her face towards the image capture device.
Patent Literature 1 discloses a technology for preventing unstable focus. According to the technology disclosed in Patent Literature 1, focus control is performed according to the contrast method when a person's face is detected by face detection. On the other hand, when a person's face is not detected, focus control is performed according to the so-called phase difference detection method while limiting the range of focus control such that a background, etc., of a captured image is not brought into focus, or in other words, such that the focus point is not set to the background, etc. Suppose a case where a face that is first being stably detected later becomes temporarily undetected, and focus control is performed according to the phase difference detection method from the point when the face becomes undetected. In such a case, when a focus point whose distance is measured according to the phase difference detection method corresponds to a background, etc., of a captured image and is not in close proximity of a focus point having been set while focus control was being performed according to the contrast method, the technology disclosed in Patent Literature 1 limits the range within which focus control can be performed according to the phase difference detection method so as to prevent unstable focus.
Patent Literature 2 discloses a technology of detecting a region in a captured image corresponding to a person (hereinafter referred to as a human region), and assuming that a region in the human region indicated by region specification information is a region in the captured image corresponding to a face of the person. Here, the region specification information is predetermined information indicating a relative position and a relative size of a face portion in a human region. One example of a technology usable in the detection of a human region (hereinafter referred to as “human detection”) is disclosed in Non-Patent Literature 1. Non-Patent Literature 1 discloses capturing a shape of a person by using a characteristic feature indicating image characteristics obtained by concatenating histogram representations of edge gradients in the image. This allows, for instance, detection of a person facing backwards. In addition, since a characteristic feature is calculated for each block according to the technology disclosed in Non-Patent Literature 1, local changes in the shape of the person are tolerated, and as a result, changes in the person's posture are tolerated to a certain extent. By performing human detection according to such a technology, a region in a captured image corresponding to a person can be detected regardless of which direction the person's face is facing in the captured image.